The present invention relates generally to nuclear reactor systems and, more particularly, to a locking device for supporting and locking fuel assemblies in place upon a support plate in a gas cooled reactor.
In gas cooled reactors, a reactor core is formed with a number of fuel assemblies containing fissile and/or fertile materials serving as a source of heat. A coolant gas such as helium, for example, is circulated between the reactor core and heat exchanger means in order to remove heat from the reactor core and employ it for doing useful work.
Within such reactors, the fuel assemblies are commonly formed as elongated tubular members which are suspended from a support plate or grid in order to facilitate circulation of the coolant gas through the fuel assemblies.
In gas cooled reactors of the type referred to above, the fuel assemblies are commonly installed and removed from beneath the grid or support plate so that the fuel assemblies must be firmly anchored to or secured upon the plate. In addition, it is necessary to assure against the fuel assemblies dropping from the support plate under normal operating conditions as well as under abnormal conditions caused for example by a seismic occurrence.
Normal forces acting upon fuel assemblies supported in such a gas cooled reactor include:
(a) downward force tending to separate the fuel assembly from the support plate resulting from the weight of the fuel assembly itself, (b) additional downward separating force resulting from a pressure drop caused by downward flow of coolant gases through the fuel assembly, and
(c) possible vibratory effects of the coolant gas flow acting upon the fuel assembly.
Abnormal forces acting upon the heat fuel assembly which must also be resisted in order to firmly secure the fuel assembly in place upon the support plate include:
(a) Lateral forces resulting from relative horizontal acceleration between the respective fuel assemblies and the support plate such as may be caused for example by seismic effects, and
(b) Upward and/or downward forces caused for example by vertical acceleration which may also result for example from a seismic occurrence.
Accordingly, there has been found to remain a need for a suitable locking device capable of supporting and locking such fuel assemblies in place within bores formed in a support plate while resisting forces of the type referred to above.